1. Field of the Invention
This invention relates to processes for disinfecting medical molding materials and molded articles made from them.
2. Statement of Related Art
In many fields of medicine, true-to-size models of organs or parts of organs have to be made on a more or less frequent basis. Thus, in pathology and in surgery, models are needed for demonstration or documentation purposes; in orthopedics, models are used for the fitting of prostheses while, in dentistry, false teeth are made from models. To make the model, a three dimensional negative of the organ in question is first prepared using molding materials and is then used as a mold for making the actual model, optionally after storage. Many materials are used to produce the negative, all of which have the property of being plastically deformable at first and then hardening after a short time to form a more or less elastic mass. Molding is carried out by pressing the organ in question into the plastic molding material and leaving it therein until the mass has hardened. The model itself is made by casting, for example by introducing mixtures of water and plaster of Paris into the negative mold.
In dentistry, there are rigid and elastic molding materials. Whereas rigid molding materials, such as plaster of Paris, zinc oxide/eugenol pastes, waxes and guttapercha are mainly used to determine the position of teeth to one another, i.e. to record bites, elastic molding materials based on synthetic or natural polymers which harden through physical or chemical crosslinking reactions are mainly used for making dental models.
At present, the most important synthetic polymers for this purpose are silicones, polyethers and polysulfides which are all chemically crosslinked. In the case of silicones, a basic distinction is drawn between condensation-crosslinking materials (these materials are hardened with organic tin or titanium compounds as catalysts which crosslink the starting polysiloxanes after the removal of terminal groups) and so-called addition-crosslinking silicone molding materials which are hardened by reaction of a vinyl-terminated polysiloxane with a polysiloxane containing SiH groups in the presence of certain platinum catalysts. In addition to polysulfides, polyether materials are also very important by virtue of their hydrophilic properties because the effective wetting, for which these properties provide, enables the tooth situation in the mouth to be particularly well reproduced, even in aqueous medium. In this case, the crosslinking reaction is based on the polymerization of epimine-terminated polyether prepolymers initiated by sulfonium salt catalysts.
The most important natural polymers are polymeric carbohydrates among which the alginates have the greatest significance. With these materials, aqueous elastic gels, which are less stable than the synthetic materials, are formed during the solidification reaction.
It is known that alginate molding materials can provide sufficiently accurate jaw impressions and are widely used because they are inexpensive to produce. This molding material is supplied to the user in the form of an alginate-containing powder which is mixed with a defined quantity of water before use. During mixing, the reactants alginic acid salt and calcium salt pass into solution, react with one another and form an insoluble, elastic hydrogel. In addition to a soluble alginic acid salt, such as potassium or sodium alginate, and a moderately soluble calcium salt, such as calcium sulfate, retarders, such as sodium phosphate or sodium pyrophosphate, fillers, such as kieselguhr, and complex transition metal fluorides, such as potassium hexafluorotitanate, are generally used. It is also of advantage to use small quantities of pyrogenic silica to obtain thixotropic behavior. To prevent dust emission from this alginate powder mixture, the mixture may be granulated by addition of soluble and insoluble organic compounds (cf. for example EP-A 0 058 203 and also DE-A 34 39 884 and DE-A 34 10 923).
The compositions of the alginate molding materials may vary within relatively wide limits. Thus, they may contain from 10 to 30% by weight sodium or potassium alginate, from 10 to 30% by weight calcium sulfate, from 0.5 to 5% by weight sodium phosphate and/or sodium pyrophosphate and, for the rest, typical fillers, flavorings and thixotropic auxiliaries. Particularly suitable fillers are kieselguhrs, sodium or potassium hexafluorotitanate and also zinc oxides.
In contrast to the alginates, molding materials based on agar-agar are reversible materials (so-called hydrocoloids) which, in principle, may be repeatedly reused. For molding, the highly aqueous agar-agar gel is converted in a water bath into the sol state, the molding material is introduced into the mouth by spoon and is converted back into a firm elastic state (gel) by the addition of cold water by spoon.
In practice, the negative mold and the actual model are generally not made by the same person. Instead, the negative mold after removal from the original is transported over more or less long distances to a model workshop where the model is made by specially trained personnel. As a result of the production process, the negative mold can be undesirably contaminated with germs, among which pathogenic germs cannot be ruled out. A particular danger in this regard in dental medicine is contamination with hepatitis viruses. Accordingly, it was proposed some time ago to disinfect the negative mold before it is passed on to eliminate any risk to people subsequently coming into contact with the mold.
However, known surface and medical instrument disinfectants could not be satisfactorily used for molding materials. The difficulties lay in the fact that a generally different spectrum of germs had to be controlled on a totally different surface, the disinfection process was not adversely to affect either the dimensional stability or the surface quality of the molding materials and the moldability of the actual model had to remain guaranteed. In the particular case of the hydrophilic materials, such as polyethers, alginates, hydrocolloids and hydrophilic silicones, exposure of the molded material to aqueous disinfectants and also alcoholic disinfectants greatly affected the quality of the model subsequently made. To overcome these difficulties, it was proposed as an alternative, for example, to add an antimicrobial agent to the molding material before molding in order thus to rule out subsequent effects on the mold (G. Lott, H. K. Gribi, Quintessence International, Vol. 19, No. 8, 571 (1981); see also EP 265 776 and DD 244 068). However, even this process does not solve all problems because many basically effective disinfectants do not develop their full effectiveness in this particular application or are incompatible with the molding material or the oral mucous membrane. In addition, contamination of the spoon in which the mold is situated is not eliminated.